It has been the practice to deposit metal onto a substrate to form a coating, using such techniques as flame, and arc plasma spraying. The powders used to make coatings were globular or spheroidal. In general the powders used for arc plasma spraying were finer than those used for flame spraying.
U.S. Pat. No. 4,124,737 discloses powders whose shape and spraying characteristics are typical of the powders employed for arc plasma spraying. These powders were atomized and should have a spheriodal shape. All the powders used for arc plasma spraying are less than 325 Tyler mesh, or finer. These powders, produced a coating that was essentially lamellar, and composed of interlocking and overlapping microscopic leaves, these leaves being mechanically bonded to each other.
U.S. Pat. No. 4,192,672 discloses an atomized powder for spray-and-fuse use. The powder had Tyler mesh sizes generally greater than 100, and for many applications it is preferred that the powder be sufficiently fine to pass through a 270 Tyler sieve. While the deposits produced by the powders of the '672 patent were dense, the density was obtained by a secondary fushion step. If this secondary fusion step were omitted the deposit would show extensive porosity.